I really could not hear gear noise from my ZF.
I have been told however that gear noise can be heard in some cases.
When I was considering a ZF rebuild, (syncros) I was considering the options you are. After weighing all the options, I decided that the best course would be to ship the ZF to one of 3 shops who have the tools, training and parts to support a ZF rebuild:
1) Steve Wilkinson
2) Cory Gheling in Wisconsin
3) Dennis Quella
Personally, I wouldn't bother with RBT.
Since your in Nor Cal - my first choice would be Wilkinson's.
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